Home
Search
Contact
Delambre Island’s flatback turtles – a 16-year population health check
November 2025
Delambre Island is a significant nesting site for flatback turtles in Australia’s North West Shelf region. The flatback turtle nesting population at Delambre Island has been monitored in collaboration with Rio Tinto for 16 years since 2008, using a multi-faceted approach. By combining nightly capture-mark-recapture (tagging) and morning track count methods, the North West Shelf Flatback Turtle Conservation Program comprehensively estimates population abundance at this rookery.
When monitoring began at Delambre Island, no turtles were already tagged. By the 2023 – 2024 season, over 70% of turtles encountered nesting at Delambre Island were tagged, indicating the program’s success and high tagging efforts.
A recent analysis of 16 years of monitoring data shows that there is an estimated 2,004 individual female flatbacks breeding annually at Delambre Island. The study “Population dynamics of flatback turtles nesting on Delambre Island, ascertained using a multi-faceted approach” was led by Dr Andrea Whiting from Biomaths Consulting, in collaboration with DBCA and Rio Tinto scientists.
The study identified that after an increase in the flatback nesting population between 2009 to 2016, there has been an overall 20% decrease in the breeding population from 2017 to 2024. This decrease is reflected in both the capture-mark-recapture and track count data.
Turtle breeding cycles are complex, and factors such as variable nesting intervals (the time between nesting seasons is approximately 2.4 years for flatback turtles), inter-nesting intervals (approximately 13.6 days between nesting within seasons) and turtles nesting at other rookeries in different seasons can potentially explain a declining trend. A high percentage (57.4%) of turtles were only seen once across the last 16 years of monitoring, which further complicates population estimates.
However, this study indicated a low survival rate of turtles after their first capture (65 – 72% survival) compared to previously captured turtles (65 – 87% survival), and lower survival probability compared to other rookeries. This may indicate higher mortality and suggests that the declining trend may be a cause for concern.
The NWSFTCP will continue monitoring at Delambre Island to identify further population abundance trends. The Program is also investigating potential causes for the decline, and adaptive management strategies to mitigate threats to the North West Shelf population.
